PyQt and Tkinter seem to not work with Blender 2.8
Both are intentionally disabled since they may cause problems with Blender in certain situations (don't ask what situations, because I haven't run into an issue yet). You can install Anaconda on your system and then delete the contents of the "python" directory in your Blender install directory. And replace it with the contents of the "C:\Anaconda3\envs\py3" folder. This completely replaces the python version that runs Blender, so be careful to download the correct version that is compatible with your version of Blender:


Python 3.6 for Blender 2.79
Python 3.7 for Blender 2.80


You may still need to install TK and PyQT separately (I can't remember what is included with Anaconda), but they should work now.